1. Technical Field
The present invention generally relates to a semiconductor device manufacturing technology, and particularly to a capacitor structure formed in a semiconductor device, and a fabrication method thereof.
2. Description of the Related Art
A semiconductor device such as an integrated circuit (IC) generally has electronic circuit elements such as transistors, capacitors, and resistors fabricated integrally on a piece of semiconductor material. The various circuit elements are connected through conductive connectors to form a complete circuit that can contain millions of individual circuit elements. In particular, capacitors are used extensively in electronic devices for storing electric charge. Capacitors essentially comprise two conductive plates separated by an insulator such as a dielectric layer.
Advances in technologies of integrating semiconductor devices have resulted in a reduced overall size of IC elements. A variety of techniques have been explored to minimize the occupied surface area of a capacitor while maintaining sufficient capacitance. One technique employs an ultra-thin film of dielectric material as a capacitor dielectric layer, but it may incur device reliability problems. Another technique utilizes a new dielectric material having a higher dielectric constant, but it may require additional processes for adapting normal semiconductor device manufacturing processes for the new material.
Meanwhile, a metal-insulator-metal (MIM) capacitor, as shown in FIG. 1, is often used in integrated circuits. A MIM capacitor is a particular type of capacitor having two metal plates sandwiching a dielectric layer. The two metal plates and the dielectric layer are parallel to a semiconductor substrate.
To form a MIM capacitor, a bottom electrode 13 and a dielectric layer 14 are formed and patterned, in sequence, on an interlevel dielectric layer 12 that insulates an upper metal layer (now shown) and a lower metal layer 11 on a semiconductor substrate 10. A top electrode 15 is then formed by depositing a conductive material, and lithographically patterning and etching the conductive material. Thus, the MIM capacitor consists of the bottom electrode 13, the dielectric layer 14, and the top electrode 15.
Because the metal plates are parallel to the substrate, a conventional MIM capacitor can be several hundred micrometers wide, which is much larger than a transistor, a memory cell, or any other elements. Thus, conventional MIM capacitors are difficult to integrate in highly integrated semiconductor devices.